High molecular weight linear polyester compositions based on bisphenols have been known to be useful in the preparation of films and fibers. These compounds, when molded into useful articles using conventional techniques, offer properties superior to those articles molded from other linear polyester compositions.
Bisphenol polyesters can be prepared by three condensation techniques, i.e., melt, homogeneous, and interfacial condensation techniques. Melt or bulk polymerization is the simplest method and in this technique, generally the reactants and catalysts are charged into a vessel and heated under vacuum. High temperatures are required and high viscosities encountered. Homogeneous or solution polymerization generally offers the advantage of being able to run the polymerization reaction at moderate temperatures and viscosities due to the presence of the solvent and catalyst. Disadvantages include necessity to remove solvent and low yield reactor volume. In the interfacial method, the reactants are dissolved in solvents which are immiscible with each other and their reaction takes place at the interface of the solvent. Advantages and disadvantages are generally similar to the solution polymerization process.
Whichever of the three condensation techniques are employed, the linear aromatic polyester produced is essentially a random polymer. As the condensation reaction proceeds, a mixture of dimers, trimers, tetramers, etc., are produced resulting in the product having an essentially random polymer characterized by an alternating microstructure of about 50%.
In the solution condensation of a bisphenol and an aromatic dicarboxylic acid halide, it is known to add the dihalide to the bisphenol or glycol or to mix the two reactants followed by addition of a suitable catalyst, and in both instances to initially employ one diol so as to form a prepolymer and thereafter add the second diol. See, e.g., Korshak et al, J. Poly. Sci., A-1, 11, 2209 (1973). The addition of the aromatic dicarboxylic acid halide to the hydroxyl-containing component is standard procedure. Copending application Serial No. 542,636 filed of even date herewith, discloses that adding the hydroxyl-containing component sequentially to the diacid halide in solution polymerization surprisingly produces high molecular weight copolyesters which have a relatively low melt viscosity and a higher degree of alternating microstructure than conventional polyesters.
This application is similar to the copending application in that a sequential addition of reactants is utilized and high molecular weight copolyesters are obtained. However, the process of this invention is not restricted to solution polymerization and the polyester produced has a significantly higher degree of alternating microstructure and a significantly higher melt viscosity compared to the products of the copending application. Thus, while the products of the copending application are useful in extrusion molding, the products of the present invention are not amenable to extrusion molding but instead can be solvent cast by techniques well known to those skilled in the art.
Accordingly, it is the object of this invention to provide a new process for the production of novel high molecular weight aromatic copolyesters having a high degree of alternating microstructure and also to provide new high molecular weight aromatic copolyesters. This and other objects of the invention will become apparent to those skilled in the art from the following detailed description.